Secondary battery comprising electrode tab provided with insulation coating layer

ABSTRACT

Provided is a secondary battery which includes an electrode assembly having an electrode tab extended from an electrode current collector, wherein the electrode tab is provided with an insulation coating layer containing an inorganic filler and a binder, the binder has an electrolyte uptake more than 0% and less than 50%, and the electrolyte uptake is determined by a predetermined method. In the secondary battery according to the present disclosure, the insulation coating layer provided in the electrode tab includes a binder having a low electrolyte uptake, and thus the insulation coating layer has improved adhesion and is prevented from detachment from the electrode tab. As a result, it is possible to maintain an excellent insulation state and to minimize an internal short-circuit in a secondary battery, thereby ensuring safety.

TECHNICAL FIELD

The present disclosure relates to a secondary battery including anelectrode tab provided with an insulation coating layer. Moreparticularly, the present disclosure relates to a secondary batteryincluding an electrode tab provided with an insulation coating layercontaining a binder having a low electrolyte uptake.

The present application claims priority to Korean Patent Application No.10-2018-0001303 filed on Jan. 4, 2018 in the Republic of Korea, thedisclosures of which including the specification and drawings areincorporated herein by reference.

BACKGROUND ART

As technological development and needs for mobile instruments have beenincreased, secondary batteries have been increasingly in demand asenergy sources. Therefore, many studies have been conducted aboutbatteries that meet various needs.

Typically, in terms of battery shapes, prismatic batteries andpouch-type batteries having a small thickness and applicable tocommercial products, such as cellular phones, are in high demand. Interms of materials, lithium secondary batteries, such as lithium cobaltpolymer batteries, having high energy density, discharge voltage andoutput stability are in high demand.

One of the main study subjects in such secondary batteries is to improvesafety. In general, a lithium secondary battery may cause explosion dueto high temperature and high voltage in the battery that may result fromabnormal operating states of the battery, such as an internalshort-circuit, overcharged state beyond the acceptable current andvoltage, exposure to high temperature and impact caused by dropping. Forexample, it is probable that such a secondary battery causes an internalshort-circuit upon impact, such as dropping or application of externalforce.

FIG. 1 is a schematic view illustrating a general structure of apouch-type secondary battery.

Referring to FIG. 1, the secondary battery 10 includes an electrodeassembly 100, a battery casing 200, electrode tabs 10, 11 and electrodeleads 20, 21.

The electrode assembly 100 includes a positive electrode plate, anegative electrode plate and a separator. The electrode assembly 100 maybe formed by stacking positive electrode plates and negative electrodeplates successively with a separator interposed between a positiveelectrode plate and a negative electrode plate. Typically, the electrodeassembly 100 may include a jelly roll (wound type) electrode assemblyformed by winding long sheet-type positive electrodes and negativeelectrodes with a separator interposed between a positive electrode anda negative electrode, a stacked (stacked type) electrode assembly formedby stacking a plurality of positive electrodes and negative electrodescut into units having a predetermined size with a separator interposedbetween a positive electrode and a negative electrode, a stacked/foldedtype electrode assembly obtained by winding bi-cells or full cellsformed by stacking predetermined units of positive electrodes andnegative electrodes with a separator interposed between a positiveelectrode and a negative electrode, or the like.

The battery casing 200 may be formed to have a size in which theelectrode assembly 100, the electrode tabs 10, 11 and electrode leads20, 21 may be received.

The electrode tabs 10, 11 are extended from the electrode assembly 100.For example, the positive electrode tab 10 is extended from the positiveelectrode plate and the negative electrode tab 11 is extended from thenegative electrode plate. Herein, when the electrode assembly 100 isformed by stacking a plurality of positive electrode plates and negativeelectrode plates, the electrode tabs 10, 11 are extended from each ofthe positive electrode plates and negative electrode plates. Herein, theelectrode tabs 10, 11 may not be exposed directly to the outside of thebattery casing 200 but may be exposed to the outside of the batterycasing 200 through the connection with another constitutional element,such as electrode leads 20, 21.

The electrode leads 20, 21 are electrically connected with the electrodetabs 10, 11 extended from the positive electrode plates and negativeelectrode plates, respectively, in a part thereof. Herein, the electrodeleads 20, 21 may be joined with the electrode tabs 10, 11 through amethod, such as welding, as shown by the shaded portion W in FIG. 1. Forexample, the electrode leads 20, 21 may be welded with the electrodetabs 10, 11 through a method, such as general resistance welding,ultrasonic wave welding, laser welding, rivet, or the like. In addition,the electrode leads 20, 21 may further include sealing tapes 30, 31 in aportion connected to the exposed part of the electrode leads.

In the case of a pouch-type secondary battery using a plurality ofpositive electrodes and negative electrodes, positive electrode tabs andnegative electrode tabs extended from the electrodes are joined with theelectrode leads through a conventional binding method.

Such a secondary battery shows a high possibility of ignition in athermal abuse test, when the temperature of the surroundings of anelectrode tab, such as a positive electrode tab, is increased, theseparator is shrunk at the corresponding portion and the positiveelectrode tab is in contact with the charged negative electrode.Particularly, ignition of the electrode tab portion becomes severe uponhigh-rate charge/discharge. Thus, it is required to reinforce the safetyof the corresponding portion.

To solve an internal short-circuit of such a battery, there has beensuggested a method for attaching an insulation member to an electrodetab. It is known that the insulation member is formed by coating anelectrode tab portion with slurry obtained by dispersing a mixturecontaining a binder used for insulation with an inorganic filler usedfor image recognition. The binder contained in such an insulation memberbecomes soft by absorbing an electrolyte during the charge/discharge ofa secondary battery, resulting in degradation of the adhesion of theinsulation member. In addition, when a thermal and mechanical abuse modeis operated at the same time, the electrode tab portion is deformed tocause detachment of the insulation member undesirably.

DISCLOSURE Technical Problem

The present disclosure is designed to solve the problems of the relatedart, and therefore the present disclosure is directed to providing asecondary battery which shows a minimized internal short-circuit and hasreinforced safety by using an electrode tab provided with an insulationcoating layer having improved adhesion to the electrode tab so as toprevent detachment.

Technical Solution

In one aspect of the present disclosure, there is provided a secondarybattery according to any one of the following embodiments.

According to the first embodiment, there is provided a secondary batterywhich includes an electrode assembly having an electrode tab extendedfrom an electrode current collector, wherein the electrode tab isprovided with an insulation coating layer containing an inorganic fillerand a binder, the binder has an electrolyte uptake more than 0% and lessthan 50%, and the electrolyte uptake is determined by the methodincluding the steps of: preparing an electrolyte including an organicsolvent containing a mixture of ethylene carbonate, propylene carbonateand diethyl carbonate, and a lithium salt; molding the binder into afilm shape, cutting the film into a predetermined size, weighing thebinder before dipping, dipping the film in the electrolyte at roomtemperature for 1 hour and removing the film from the electrolyte, andweighing the binder after dipping; and calculating the electrolyteuptake by using the following Formula 1:

$\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

According to the second embodiment, there is provided a secondarybattery which includes an electrode assembly having an electrode tabextended from an electrode current collector, wherein the electrode tabis provided with an insulation coating layer containing an inorganicfiller and a binder, the binder has an electrolyte uptake more than 0%and less than 150%, and the electrolyte uptake is determined by themethod including the steps of: preparing an electrolyte including anorganic solvent containing a mixture of ethylene carbonate, propylenecarbonate and propyl propionate, and a lithium salt; molding the binderinto a film shape, cutting the film into a predetermined size, weighingthe binder before dipping, dipping the film in the electrolyte at roomtemperature for 1 hour and removing the film from the electrolyte, andweighing the binder after dipping; and calculating the electrolyteuptake by using the following Formula 1:

$\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

According to the third embodiment, there is provided the secondarybattery as defined in the first embodiment or the second embodiment,wherein ethylene carbonate is used in an amount of 20 parts by weight ormore based on 100 parts by weight of the total weight of the organicsolvent.

According to the fourth embodiment, there is provided the secondarybattery as defined in the third embodiment, wherein ethylene carbonate,propylene carbonate and diethyl carbonate are mixed at a weight ratio of30:20:50.

According to the fifth embodiment, there is provided the secondarybattery as defined in the third embodiment, wherein ethylene carbonate,propylene carbonate and propyl propionate are mixed at a weight ratio of30:10:60.

According to the sixth embodiment, there is provided the secondarybattery as defined in any one of the first to the fifth embodiments,wherein the binder includes styrene-butadiene rubber containing arepeating unit derived from a monomer having a crosslinkable group.

According to the seventh embodiment, there is provided the secondarybattery as defined in any one of the first to the sixth embodiments,wherein the binder includes styrene-butadiene rubber containing 12 partsby weight or less of a repeating unit derived from an acrylic acid (AA)monomer.

According to the eighth embodiment, there is provided the secondarybattery as defined in the seventh embodiment, wherein the binder is astyrene-butadiene-acrylic acid copolymer.

According to the ninth embodiment, there is provided the secondarybattery as defined in any one of the first to the eighth embodiments,wherein the binder includes a fluoride-based binder polymer containing90 parts by weight or more of a repeating unit derived from a vinylidenefluoride (VdF) monomer.

According to the tenth embodiment, there is provided the secondarybattery as defined in the ninth embodiment, wherein the fluoride-basedbinder polymer is polyvinylidene fluoride.

According to the eleventh embodiment, there is provided the secondarybattery as defined in any one of the first to the tenth embodiments,wherein the insulation coating layer includes the inorganic filler andthe binder at a weight ratio of 5:95-80:20.

According to the twelfth embodiment, there is provided the secondarybattery as defined in any one of the first to the eleventh embodiments,wherein the inorganic filler includes SiO₂, TiO₂, Al₂O₃, AlOOH, γ-AlOOH,ZrO₂, SnO₂, CeO₂, MgO, CaO, ZnO, Y₂O₃, Pb(Zr,Ti)O₃ (PZT),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃(PMN-PT), BaTiO₃, hafnia (HfO₂), SrTiO₃ or a mixture thereof.

According to the thirteenth embodiment, there is provided the secondarybattery as defined in any one of the first to the twelfth embodiments,wherein the insulation coating layer further includes a dispersingagent.

According to the fourteenth embodiment, there is provided the secondarybattery as defined in the thirteenth embodiment, wherein the insulationcoating layer includes the dispersing agent in an amount of 0.1-5 wt %based on the weight of the inorganic filler.

According to the fifteenth embodiment, there is provided the secondarybattery as defined in any one of the first to the fourteenthembodiments, wherein the electrode tab is a positive electrode tab.

Advantageous Effects

In the secondary battery according to the present disclosure, theinsulation coating layer provided in the electrode tab includes a binderhaving a low electrolyte uptake, and thus the insulation coating layerhas improved adhesion and is prevented from detachment from theelectrode tab. As a result, it is possible to maintain an excellentinsulation state and to minimize an internal short-circuit in asecondary battery, thereby ensuring safety.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a general structure of aconventional pouch-type secondary battery.

FIG. 2 is a schematic sectional view illustrating the secondary batteryaccording to an embodiment of the present disclosure.

BEST MODE

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation. Therefore, thedescription proposed herein is just a preferable example for the purposeof illustrations only, not intended to limit the scope of thedisclosure, so it should be understood that other equivalents andmodifications could be made thereto without departing from the scope ofthe disclosure.

In one aspect, there is provided a secondary battery including anelectrode assembly having an electrode tab extended from an electrodecurrent collector, particularly including an electrode assembly whichincludes a positive electrode having a positive electrode tab extendedfrom a positive electrode current collector, a negative electrode havinga negative electrode tab extended from a negative electrode currentcollector, and a separator interposed between the positive electrode andthe negative electrode.

According to an embodiment of the present disclosure, the electrode tabis provided with an insulation coating layer containing an inorganicfiller and a binder.

The binder is an ingredient which functions to impart insulationproperty and is used for the adhesion between inorganic fillers or theadhesion between the inorganic filler and the electrode tab, and ischaracterized in that it has an electrolyte uptake more than 0% and lessthan 50%, wherein the electrolyte uptake is determined by the methodincluding the steps of: preparing an electrolyte including an organicsolvent containing a mixture of ethylene carbonate, propylene carbonateand diethyl carbonate, and a lithium salt; molding the binder into afilm shape, cutting the film into a predetermined size, weighing thebinder before dipping, dipping the film in the electrolyte at roomtemperature (25° C.) for 1 hour and removing the film from theelectrolyte, and weighing the binder after dipping; and calculating theelectrolyte uptake by using the following Formula 1:

$\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

According to an embodiment of the present disclosure, the electrolyteuptake may be more than 0% and less than 50%, 3-47%, or 6-47%.

Herein, the electrolyte may include ethylene carbonate (EC) in an amountof 20 parts by weight or more based on 100 parts by weight of the totalorganic solvent.

According to an embodiment of the present disclosure, ethylene carbonate(EC), propylene carbonate (PC) and diethyl carbonate (DEC) may be mixedat a weight ratio of 30:20:50-20:10:70, preferably 30:20:50.

According to an embodiment of the present disclosure, the secondarybattery includes an electrode assembly and an electrolyte injectedthereto, wherein the electrolyte may be the same as the electrolyte usedfor determination of the electrolyte uptake.

Meanwhile, it is preferred to substitute diethyl carbonate (DEC) withpropyl propionate (PP) in the ingredients of the organic solventcontained in the electrolyte in order to realize a secondary batterycapable of operating at a high voltage. For example, decomposition ofdiethyl carbonate (DEC) is accelerated upon operation at a high voltage,while a secondary battery using an electrolyte containing propylpropionate (PP) at a predetermined ratio can be operated at a highvoltage of 4.25V or more, particularly 4.4V or more, withoutdecomposition. When a secondary battery capable of operating at a highvoltage is to be realized, the binder shows an electrolyte uptake morethan 0% and less than 150%, wherein the electrolyte uptake is determinedby the method including the steps of: preparing an electrolyte includingan organic solvent containing a mixture of ethylene carbonate, propylenecarbonate and propyl propionate, and a lithium salt; molding the binderinto a film shape, cutting the film into a predetermined size, weighingthe binder before dipping, dipping the film in the electrolyte at roomtemperature (25° C.) for 1 hour and removing the film from theelectrolyte, and weighing the binder after dipping; and calculating theelectrolyte uptake by using the following Formula 1:

$\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

According to an embodiment of the present disclosure, the electrolyteuptake may be more than 0% and less than 150%, 3-130%, or 12-127%.

Herein, the electrolyte may include ethylene carbonate (EC) in an amountof 20 parts by weight or more based on 100 parts by weight of the totalorganic solvent.

According to an embodiment of the present disclosure, ethylene carbonate(EC), propylene carbonate (PC) and propyl propionate (PP) may be mixedat a weight ratio of 30:20:50-20:10:70, preferably 25:10:65 or 30:10:60.

According to an embodiment of the present disclosure, the secondarybattery includes an electrode assembly and an electrolyte injectedthereto, wherein the electrolyte may be the same as the electrolyte usedfor determination of the electrolyte uptake.

The electrolyte uptake of the binder determined as described above is anindex indicating electrolyte resistance, wherein a binder having a lowelectrolyte uptake shows high adhesion even in a state wetted with anelectrolyte. Therefore, such a binder can alleviate a decrease inadhesion caused by the electrolyte absorption of the binder contained inthe insulation coating layer during charge/discharge of a secondarybattery.

As a result, it is possible to inhibit detachment of the insulationcoating layer. On the other hand, an insulation coating layer containinga binder having a high electrolyte uptake undergoes a decrease inadhesion, and thus may be detached from an electrode tab with ease.

Binders having a low electrolyte uptake may include styrene-butadienerubber including a styrene monomer-derived repeating unit and abutadiene monomer-derived repeating unit at a weight ratio of70:30-30:70. Particularly, such styrene-butadiene rubber includes arepeating unit derived from a styrene monomer having a hydrophobic groupwithin the above-defined range, and thus has a controlled electrolyteuptake.

In addition, the combined weight of the styrene monomer-derivedrepeating unit with the butadiene monomer-derived repeating unit may be30-100 w % or 30-70 wt % based on the total weight of thestyrene-butadiene rubber. Within the above-defined range, it is possibleto control the electrolyte uptake.

Particular examples of the styrene monomer include styrene,α-methylstyrene, p-methylstyrene, 3-methylstyrene, 4-methylstyrene,4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene,4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, and derivativesand mixtures thereof. Particular examples of the butadiene monomerinclude 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, and derivatives and mixtures thereof.

If desired, the styrene-butadiene rubber may further include a repeatingunit derived from a monomer having a crosslinkable group. Herein, therepeating unit derived from a monomer having a crosslinkable group isused preferably in an amount of 12 parts by weight or less based on thetotal weight of the styrene-butadiene rubber.

According to an embodiment of the present disclosure, the binder mayinclude styrene-butadiene rubber containing 12 parts by weight or lessof a repeating unit derived from an acrylic acid (AA) monomer. When thecontent of the repeating unit derived from an acrylic acid monomer is 12parts by weight or less, it is possible to reduce the problem ofdisintegration of a positive electrode at a high potential caused by alow electrolyte uptake.

Particularly, the binder may be a styrene-butadiene-acrylic acidcopolymer.

According to an embodiment of the present disclosure, the binder mayinclude a fluoride-based binder polymer containing 90 parts by weight ormore, or 95 parts by weight of more of a repeating unit derived from avinylidene fluoride (VdF) monomer.

When the fluoride-based binder polymer includes a vinylidene fluoridemonomer within the above-defined range, it is possible to control theelectrolyte uptake of the binder and to reduce the problem ofdisintegration of a positive electrode at a high potential.

Particularly, the fluoride-based binder polymer may be polyvinylidenefluoride.

According to an embodiment of the present disclosure, the insulationcoating layer may be formed by coating an electrode tab with slurryincluding an inorganic filler in combination with the above-describedbinder and optionally further containing a dispersing agent.

The inorganic filler functions to realize a color so that the insulationcoating layer may allow image recognition and enables one to recognizethe position, size and thickness of an insulation coating layer providedin an electrode tab easily by the naked eyes. Non-limiting examples ofthe inorganic filler may include SiO₂, TiO₂, Al₂O₃, AlOOH, γ-AlOOH,ZrO₂, SnO₂, CeO₂, MgO, CaO, ZnO, Y₂O₃, Pb(Zr,Ti)O₃ (PZT),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃(PMN-PT), BaTiO₃, hafnia (HfO₂), SrTiO₃, and mixtures thereof.

In the insulation coating layer according to the present disclosure, theinorganic filler and binder may be used at a weight ratio of 5:95-80:20or 10:90-50:50. Within the above-defined range, it is possible to obtainsufficient adhesion between inorganic fillers, sufficient adhesionbetween the insulation coating layer and the electrode tab and a desiredinsulation effect.

The dispersing agent is an ingredient which is adsorbed to the inorganicfiller in the slurry for forming an insulation coating layer to assistdispersion of inorganic materials and to improve slurry stability.Herein, ‘slurry stability’ refers to a property of slurry with which theinorganic filler contained in the slurry is not settled for a long timebut is dispersed and distributed homogeneously in the whole slurry afterthe slurry is applied.

Herein, ‘long time’ may refer to a period required for the slurry to bedried, for example.

Such a dispersing agent may be exemplified by a cellulose-based compoundand non-limiting examples thereof include carboxymethyl cellulose,carboxyethyl cellulose or a derivative thereof, such as a compoundsubstituted with a cation, such as ammonium ion or primary metal ion.

In the insulation coating layer according to the present disclosure, thedispersing agent may be used in an amount of 0.1-5 wt % based on theweight of the inorganic filler. Within the above-defined range, it ispossible to prevent degradation of coating properties caused by anincrease in viscosity and to inhibit rapid sediment of the inorganicfiller.

Meanwhile, particular examples of the solvent or dispersion medium usedfor the slurry for forming an insulation coating layer may include:water; alcohols, such as methanol, ethanol, propanol and butanol;ketones, such as acetone and phenylethyl ketone; ethers, such as methylethyl ether, diethyl ether and diisoamyl ether; lactones, such asgamma-butyrolactone; N-methyl-2-pyrrolidone (NMP); lactams, such asbeta-lactam; cyclic aliphatic compounds, such as cyclopentane andcyclohexane; aromatic hydrocarbons, such as benzene and toluene; esters,such as methyl lactate and ethyl lactate; or the like. Among them, wateris particularly suitable as an eco-friendly dispersion medium. Inaddition, N-methyl-2-pyrrolidone similar to the conventional anodiccoating may be used suitably. The content of solvent is not particularlylimited but is determined considering the dispersibility of theinorganic filler, coating feasibility, drying time, or the like.

According to an embodiment of the present disclosure, the insulationcoating layer may be formed by applying the slurry for an insulationcoating layer to the electrode tab portion of an electrode currentcollector, followed by drying, after slurry for an electrode activematerial layer is applied to and dried on the electrode collector toform an electrode active material layer.

In a variant, according to another embodiment of the present disclosure,the insulation coating layer may be formed by applying the slurry for aninsulation coating layer to the electrode tab portion of an electrodecurrent collector, followed by drying, to form an insulation coatinglayer, and then applying slurry for an electrode active material layerto the remaining portion of the electrode current collector having noinsulation coating layer, followed by drying, to form an electrodeactive material layer.

In another variant, according to still another embodiment of the presentdisclosure, the insulation coating layer may be formed by applyingslurry for an insulation coating layer to the electrode tab portion ofan electrode current collector and drying the slurry, and applyingslurry for an electrode active material layer to the remaining portionof the electrode current collector having no insulation coating layerand drying the slurry, at the same time.

Coating processes for forming the insulation coating layer may includebut are not limited to: dipping, spray coating, spin coating, rollcoating, die coating, gravure printing, bar coating, or the like.

According to an embodiment of the present disclosure, the insulationcoating layer is formed preferably to have a thickness smaller than thethickness of each electrode active material layer. For example, thethickness of the insulation coating layer may be determined to be about5-100% or 10-50% of the thickness of each electrode active materiallayer. When the insulation coating layer has a thickness smaller thanthe lower limit, it is difficult to expect an electrical insulationeffect. When the insulation coating layer has a thickness larger thanthe upper limit, the volume of an electrode tab is increasedundesirably.

FIG. 2 is a schematic view illustrating the pouch-type secondary batteryaccording to an embodiment of the present disclosure. In FIG. 2, aninsulation coating layer C is formed in the positive electrode tab ofthe pouch-type secondary battery as shown in FIG. 1.

Since it is highly probable that the positive electrode tab is incontact preferentially with the negative electrode (current collector oractive material) of the electrode assembly upon external impact causedby dropping, the slurry for forming an insulation coating layeraccording to the present disclosure is coated preferably on the positiveelectrode tab. However, insulation coating layers may be formed on bothof the positive electrode tab and negative electrode tab.

In addition, only one positive electrode tab is shown in FIG. 2.However, the insulation coating layer may be formed in each of multiplepositive electrode tabs and negative electrode tabs in the case of asecondary battery using multiple positive electrodes and negativeelectrodes and thus including multiple positive electrode tabs andnegative electrode tabs.

Further, the insulation coating layer may be formed partially or totallyin the electrode tab, according to the present disclosure.

In a non-limiting example of the insulation coating layer formedpartially in the electrode tab, the insulation coating layer may beformed in the electrode tab portion adjacent to the electrode assembly,wherein it is highly probable that the electrode tab is in contact withthe electrode assembly. Otherwise, the insulation coating layer may beformed in a portion of the electrode tab except the connection with anelectrode lead.

The insulation coating layer may be formed totally in the electrode tab.Since the electrical insulation coating layer is molten and removedduring welding for the connection with an electrode lead, it is possibleto form an insulation coating layer in the whole electrode tab. In termsof process feasibility, it is preferred to form the insulation coatinglayer totally in the electrode tab.

According to the present disclosure, electrode assemblies formed bystacking positive electrodes and negative electrodes with a separatorbetween a positive electrode and a negative electrode may be stacked toprovide a stacked secondary battery or a stacked-folded secondarybattery, or may be wound into a jelly-roll shape to provide a secondarybattery.

The battery casing may have various shapes, such as a pouch-type casingor prismatic casing.

For example, the positive electrode is obtained by applying a mixture ofa positive electrode active material, a conductive material and a binderonto a positive electrode current collector, followed by drying. Ifdesired, a filler may be further added to the mixture.

Particular examples of the positive electrode active material mayinclude, but are not limited to: layered compounds such as lithiumcobalt oxide (LiCoO₂) and lithium nickel oxide (LiNiO₂), or thosecompounds substituted with one or more transition metals; lithiummanganese oxides such as those represented by the chemical formula ofLi_(1+x)Mn_(2-x)O₄ (wherein x is 0-0.33), LiMnO₃, LiMn₂O₃ and LiMnO₂;lithium copper oxide (Li₂CuO₂); vanadium oxides such as LiV₃O, LiFe₃O₄,V₂O₅ or Cu₂V₂O₇; Ni-site type lithium nickel oxides represented by thechemical formula of LiNi_(1-x)M_(x)O₂ (wherein M is Co, Mn, Al, Cu, Fe,Mg, B or Ga, and x is 0.01-0.3); lithium manganese composite oxidesrepresented by the chemical formula of LiMn_(2-x)MxO₂ (wherein M=Co, Ni,Fe, Cr, Zn or Ta, and x=0.01-0.1) or Li₂Mn₃MO (wherein M=Fe, Co, Ni, Cuor Zn); LiMn₂O₄ in which Li is partially substituted with an alkalineearth metal ion; disulfide compounds; Fe₂(MoO₄)₃; or the like.

The positive electrode current collector is formed to have a thicknessof 3-500 μm. The positive electrode current collector is notparticularly limited, as long as it causes no chemical change in thecorresponding battery and has high conductivity. Particular examples ofthe positive electrode current collector may include stainless steel;aluminum; nickel; titanium; baked carbon; aluminum or stainless steelsurface-treated with carbon, nickel, titanium or silver; or the like. Itis possible to increase the adhesion of a positive electrode activematerial by forming fine surface irregularities on the surface of acurrent collector. The positive electrode current collector may havevarious shapes, such as a film, sheet, foil, net, porous body, foam anda non-woven web body.

The conductive material is added generally in an amount of 1-50 wt %based on the total weight of the mixture including the positiveelectrode active material. The conductive material is not particularlylimited, as long as it causes no chemical change in the correspondingbattery and has conductivity. Particular examples of the conductivematerial include: graphite, such as natural graphite or artificialgraphite; carbon black, such as carbon black, acetylene black, Ketjenblack, channel black, furnace black, lamp black or thermal black;conductive fibers, such as carbon fibers or metallic fibers; metalpowder, such as carbon fluoride, aluminum or nickel powder; conductivewhisker, such as zinc oxide or potassium titanate; conductive metaloxide, such as titanium oxide; and conductive materials, such aspolyphenylene derivatives.

The binder is an ingredient which assists binding between the electrodeactive material and the conductive material and binding to the currentcollector. In general, the binder is added in an amount of 1-50 wt %based on the total weight of the mixture including the positiveelectrode active material. Particular examples of the binder includepolyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose(CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene,ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrenebutyrene rubber, fluororubber, various copolymers, or the like.

The filler is an ingredient inhibiting swelling of the positiveelectrode and is used optionally. The filler is not particularlylimited, as long as it causes no chemical change in the correspondingbattery and is a fibrous material. Particular examples of the fillerinclude olefinic polymers, such as polyethylene or polypropylene; andfibrous materials, such as glass fibers or carbon fibers.

The negative electrode is obtained by applying a negative electrodeactive material onto a negative electrode current collector, followed bydrying. If desired, the negative electrode material may further includethe above-described ingredients.

The negative electrode current collector is formed to have a thicknessof 3-500 μm. The negative electrode current collector is notparticularly limited, as long as it causes no chemical change in thecorresponding battery and has conductivity. Particular examples of thenegative electrode current collector may include copper; stainlesssteel; aluminum; nickel; titanium; baked carbon; copper or stainlesssteel surface-treated with carbon, nickel, titanium or silver;aluminum-cadmium alloy; or the like. Similarly to the positive electrodecurrent collector, it is possible to increase the adhesion of a negativeelectrode active material by forming fine surface irregularities on thesurface of a current collector. The negative electrode current collectormay have various shapes, such as a film, sheet, foil, net, porous body,foam and a non-woven web body.

Particular examples of the negative electrode active material include:carbon such as non-graphitizable carbon or graphite-based carbon; metalcomposite oxides, such as Li_(x)Fe₂O₃(0≤x≤1), Li_(x)WO₂(0≤x≤1),Sn_(x)Me_(1-x)Me′_(y)O_(z) (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si,elements of Group 1, 2 or 3 in the Periodic Table, halogen; 0<x≤1;1≤y≤3; 1≤z≤8); lithium metal; lithium alloy; silicon-based alloy;tin-based alloy; metal oxides, such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃,Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄ and Bi₂O₅;conductive polymers, such as polyacetylene; Li—Co—Ni type materials;titanium oxide; lithium titanium oxide.

The separator is interposed between the positive electrode and thenegative electrode. An insulating thin film having high ion permeabilityand mechanical strength is used as the separator. The separatorgenerally has a pore diameter of 0.01-10 μm and a thickness of 5-300 μm.Particular examples of the separator include sheets or nonwoven websmade of olefinic polymers, such as polypropylene having chemicalresistance and hydrophobic property; glass fibers or polyethylene, orthe like.

According to an embodiment of the present disclosure, the lithium saltcontained in the electrolyte is an ingredient that may be dissolved withease in a mixed organic solvent of ethylene carbonate, propylenecarbonate and diethyl carbonate or a mixed organic solvent of ethylenecarbonate, propylene carbonate and propyl propionate. Particularexamples of the lithium salt include LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,(CF₃SO₂)₂NLi, lithium chloroborate, lithium lower aliphatic carboxylate,lithium tetraphenyl borate, imide, or the like.

In addition, the electrolyte may further include pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme,triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone iminedyes, N-substituted oxazolidinone, N,N-substituted imidazolidine,ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethaoland aluminum trichloride in order to improve the charge/dischargecharacteristics, flame resistance, or the like. Optionally, theelectrolyte may further include a halogen-containing solvent, such ascarbon tetrachloride or trifluoroethylene, in order to impartnon-combustibility. The electrolyte may further include carbon dioxidegas in order to improve the high-temperature storage characteristics.

The present disclosure has been described in detail with reference tothe accompanying drawings. However, it should be understood that thedetailed description and specific examples, while indicating preferredembodiments of the disclosure, are given by way of illustration only,since various changes and modifications within the scope of thedisclosure will become apparent to those skilled in the art from thisdetailed description. Therefore, it should be understood that theabove-described embodiments are for illustrative purposes only and arenon-limiting.

Example 1

A dispersing agent (carboxymethyl cellulose, BG-L01, Global Leader Chem)was dissolved in water as a solvent and alumina (LS235, Nippon LightMetal Company) as an inorganic filler was added thereto at a weightratio of the dispersing agent to the inorganic filler of 0.5 wt %. Tothe dispersed alumina slurry, a binder, H78 (styrene (ST):butadiene(BD):acrylic acid (AA)=57:35:8, LG Chem) was added at a weight ratio ofalumina:binder of 20:80 to obtain slurry for an insulation coatinglayer. Herein, the binder had an electrolyte uptake of 47% to theelectrolyte obtained by dissolving 1M LiPF₆ in a mixed solventcontaining ethylene carbonate (EC), propylene carbonate (PC) and diethylcarbonate (DEC) at a ratio of 30:20:50 (weight ratio).

Herein, the electrolyte uptake of the binder was determined as follows:The binder was molded into a film shape, cut into a predetermined sizeand then weighed. The film was dipped in the electrolyte at roomtemperature (25° C.) for 1 hour and weighed. Then, the electrolyteuptake was calculated according to the following Formula 1:

$\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

The slurry was applied to the electrode tab portion of a positiveelectrode current collector so that the coating might have a thicknesscorresponding to 30% of the thickness of the positive electrode activematerial layer and a width of 1.7 mm to obtain a positive electrodeprovided with an insulation coating layer.

The positive electrode was used and the electrolyte (EC:PC:DEC=30:20:50)was injected to obtain a secondary battery.

Example 2

A dispersing agent (carboxymethyl cellulose, BG-L01, Global Leader Chem)was dissolved in water as a solvent and alumina (LS235, Nippon LightMetal Company) as an inorganic filler was added thereto at a weightratio of the dispersing agent to the inorganic filler of 0.5 wt %. Tothe dispersed alumina slurry, a binder, H78 (styrene (ST):butadiene(BD):acrylic acid (AA)=57:35:8, LG Chem) was added at a weight ratio ofalumina:binder of 2:8 to obtain coating slurry. Herein, the binder hadan electrolyte uptake of 127% to the electrolyte obtained by dissolving1M LiPF₆ in a mixed solvent containing ethylene carbonate (EC),propylene carbonate (PC) and propyl propionate (PP) at a ratio of30:10:60 (weight ratio). Herein, the electrolyte uptake of the binderwas determined as follows: The binder was molded into a film shape, cutinto a predetermined size and then weighed. The film was dipped in theelectrolyte at room temperature (25° C.) for 1 hour and weighed. Then,the electrolyte uptake was calculated according to the above Formula 1.

The slurry was applied to the electrode tab portion of a positiveelectrode current collector so that the coating might have a thicknesscorresponding to 30% of the thickness of the positive electrode activematerial layer and a width of 1.7 mm to obtain a positive electrodeprovided with an insulation coating layer.

The positive electrode was used and the electrolyte (EC:PC:PP=30:10:60)was injected to obtain a secondary battery.

Example 3

A secondary battery was obtained in the same manner as Example 1, exceptthat BD53 (ST:BD=62:38, LG Chem, electrolyte uptake (EC:PC:DEC=30:20:50)6%) was used as a binder. Herein, the electrolyte uptake of the binderwas determined as follows: The binder was molded into a film shape, cutinto a predetermined size and then weighed. The film was dipped in theelectrolyte at room temperature (25° C.) for 1 hour and weighed. Then,the electrolyte uptake was calculated according to the above Formula 1.

Example 4

A secondary battery was obtained in the same manner as Example 2, exceptthat BD53 (ST:BD=62:38, LG Chem, electrolyte uptake (EC:PC:PP=30:10:60)48%) was used as a binder. Herein, the electrolyte uptake of the binderwas determined as follows: The binder was molded into a film shape, cutinto a predetermined size and then weighed. The film was dipped in theelectrolyte at room temperature (25° C.) for 1 hour and weighed. Then,the electrolyte uptake was calculated according to the above Formula 1.

Example 5

A secondary battery was obtained in the same manner as Example 2, exceptthat N-methyl-2-pyrrolidone (NMP) was used as a solvent andpolyvinylidene fluoride (KF1100, Kureha, electrolyte uptake(EC:PC:PP=30:10:60) 12%) was used as a binder.

Herein, the electrolyte uptake of the binder was determined as follows:The binder was molded into a film shape, cut into a predetermined sizeand then weighed. The film was dipped in the electrolyte at roomtemperature (25° C.) for 1 hour and weighed. Then, the electrolyteuptake was calculated according to the above Formula 1.

Example 6

A secondary battery was obtained in the same manner as Example 5, exceptthat a polyvinylidene fluoride copolymer (8200, Kureha, electrolyteuptake (EC:PC:PP=30:10:60) 17%) was used as a binder.

Herein, the electrolyte uptake of the binder was determined as follows:The binder was molded into a film shape, cut into a predetermined sizeand then weighed. The film was dipped in the electrolyte at roomtemperature (25° C.) for 1 hour and weighed. Then, the electrolyteuptake was calculated according to the above Formula 1.

Comparative Example 1

A secondary battery was obtained in the same manner as Example 1, exceptthat SU006 (AA alone, Toyo Ink., electrolyte uptake (EC:PC:DEC=30:20:50)105%) was used as a binder. Herein, the electrolyte uptake of the binderwas determined as follows: The binder was molded into a film shape, cutinto a predetermined size and then weighed. The film was dipped in theelectrolyte at room temperature (25° C.) for 1 hour and weighed. Then,the electrolyte uptake was calculated according to the above Formula 1.

Comparative Example 2

A secondary battery was obtained in the same manner as Example 1, exceptthat H79 (ST:BD:AA=52:31:17, LG Chem, electrolyte uptake(EC:PC:DEC=30:20:50) 73%) was used as a binder. Herein, the electrolyteuptake of the binder was determined as follows: The binder was moldedinto a film shape, cut into a predetermined size and then weighed. Thefilm was dipped in the electrolyte at room temperature (25° C.) for 1hour and weighed. Then, the electrolyte uptake was calculated accordingto the above Formula 1.

Comparative Example 3

A secondary battery was obtained in the same manner as Example 2, exceptthat H79 (ST:BD:AA=52:31:17, LG Chem, electrolyte uptake(EC:PC:PP=30:10:60) 174%) was used as a binder. Herein, the electrolyteuptake of the binder was determined as follows: The binder was moldedinto a film shape, cut into a predetermined size and then weighed. Thefilm was dipped in the electrolyte at room temperature (25° C.) for 1hour and weighed. Then, the electrolyte uptake was calculated accordingto the above Formula 1.

Comparative Example 4

Slurry for an insulation coating layer was prepared in the same manneras Example 1, except that crosslinked Li-PAA (Aekyung Chem., electrolyteuptake (EC:PC:DEC=30:20:50) 0%) was used as a binder and no dispersingagent was used. The prepared slurry for a positive electrode insulationcoating layer was applied and dried first, and then slurry for apositive electrode active material layer was applied to obtain asecondary battery including a positive electrode provided with aninsulation coating layer.

Herein, the electrolyte uptake of the binder was determined as follows:The binder was molded into a film shape, cut into a predetermined sizeand then weighed. The film was dipped in the electrolyte at roomtemperature (25° C.) for 1 hour and weighed. Then, the electrolyteuptake was calculated according to the above Formula 1.

Test Example 1

Five samples were prepared for each of the secondary batteries accordingto Examples 1-6 and Comparative Examples 1-4. Then a dropping test wascarried out 100 times from a height of 1 m and a hot box test wasperformed by allowing each sample to stand at 140° C. for 1 hour.

As a result, all the samples according to Examples 1-6 and ComparativeExample 4 passed the hot box test. On the contrary, in the case ofComparative Example 1, ignition occurred in 3 samples of 5 samples. Inthe case of Comparative Examples 2 and 3, ignition occurred in 1 sampleof 5 samples. In other words, it is thought that since ComparativeExamples 1-3 use a binder having a high electrolyte uptake for formingan insulation coating layer, the insulation coating layer is detachedfrom the electrode tab due to a decrease in adhesion to cause aninternal short-circuit.

Test Example 2

Each of the secondary batteries according to Examples 1-6 andComparative Examples 1-4 was determined for 0.2 C discharge capacity.

As a result, each of Examples 1-6 and Comparative Examples 1-3 realizeddesigned capacity but Comparative Example 4 showed degradation ofcapacity by 2.1% based on designed capacity. It is thought that lithiumions cannot be transported in the region where the insulation coatinglayer is overlapped with the positive electrode to cause degradation ofcapacity.

1. A secondary battery comprising an electrode assembly having anelectrode tab extended from an electrode current collector, wherein theelectrode tab comprises an insulation coating layer containing aninorganic filler and a binder, an electrolyte uptake of the binder ismore than 0% and less than 50%, and the electrolyte uptake is determinedby a method comprising: preparing an electrolyte comprising an organicsolvent containing a mixture of ethylene carbonate, propylene carbonateand diethyl carbonate, and a lithium salt; molding the binder into afilm shape, cutting the film into a predetermined size, weighing thebinder in the film shape before dipping, dipping the film in theelectrolyte at room temperature for 1 hour and removing the film fromthe electrolyte, and weighing the binder in the film shape afterdipping; and calculating the electrolyte uptake by using the followingFormula 1: $\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$
 2. A secondary battery comprising an electrode assemblyhaving an electrode tab extended from an electrode current collector,wherein the electrode tab comprises an insulation coating layercontaining an inorganic filler and a binder, an electrolyte uptake ofthe binder is more than 0% and less than 150%, and the electrolyteuptake is determined by a method comprising: preparing an electrolytecomprising an organic solvent containing a mixture of ethylenecarbonate, propylene carbonate and propyl propionate, and a lithiumsalt; molding the binder into a film shape, cutting the film into apredetermined size, weighing the binder in the film shape beforedipping, dipping the film in the electrolyte at room temperature for 1hour and removing the film from the electrolyte, and weighing the binderin the film shape after dipping; and calculating the electrolyte uptakeby using the following Formula 1: $\begin{matrix}{\frac{{Weight}\mspace{14mu} {after}\mspace{14mu} {dipping}}{{Weight}\mspace{14mu} {before}\mspace{14mu} {dipping}} \times 100\; (\%)} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$
 3. The secondary battery according to claim 2, wherein, inthe preparing the electrolyte, ethylene carbonate is used in an amountof 20 parts by weight or more based on 100 parts by weight of the totalweight of the organic solvent.
 4. (canceled)
 5. The secondary batteryaccording to claim 3, wherein, in the preparing the electrolyte,ethylene carbonate, propylene carbonate and propyl propionate are mixedat a weight ratio of 30:10:60.
 6. The secondary battery according toclaim 2, wherein the binder comprises styrene-butadiene rubbercontaining a repeating unit comprising a monomer having a crosslinkablegroup.
 7. The secondary battery according to claim 2, wherein the bindercomprises styrene-butadiene rubber containing 12 parts by weight or lessof a repeating unit comprising an acrylic acid (AA) monomer.
 8. Thesecondary battery according to claim 7, wherein the binder comprises astyrene-butadiene-acrylic acid copolymer.
 9. The secondary batteryaccording to claim 2, wherein the binder comprises a fluoride-containingbinder polymer containing 90 parts by weight or more of a repeating unitcomprising a vinylidene fluoride (VdF) monomer.
 10. The secondarybattery according to claim 9, wherein the fluoride-containing binderpolymer comprises polyvinylidene fluoride.
 11. The secondary batteryaccording to claim 2, wherein the insulation coating layer comprises theinorganic filler and the binder at a weight ratio of 5:95-80:20. 12-14.(canceled)
 15. The secondary battery according to claim 2, wherein theelectrode tab is a positive electrode tab.
 16. The secondary batteryaccording to claim 1, wherein, in the preparing the electrolyte,ethylene carbonate is used in an amount of 20 parts by weight or morebased on 100 parts by weight of the total weight of the organic solvent.17. The secondary battery according to claim 16, wherein, in thepreparing the electrolyte, ethylene carbonate, propylene carbonate anddiethyl carbonate are mixed at a weight ratio of 30:20:50.
 18. Thesecondary battery according to claim 1, wherein the binder comprisesstyrene-butadiene rubber containing a repeating unit comprising amonomer having a crosslinkable group.
 19. The secondary batteryaccording to claim 1, wherein the binder comprises styrene-butadienerubber containing 12 parts by weight or less of a repeating unitcomprising an acrylic acid (AA) monomer.
 20. The secondary batteryaccording to claim 19, wherein the binder comprises astyrene-butadiene-acrylic acid copolymer.
 21. The secondary batteryaccording to claim 1, wherein the binder comprises a fluoride-containingbinder polymer containing 90 parts by weight or more of a repeating unitcomprising a vinylidene fluoride (VdF) monomer.
 22. The secondarybattery according to claim 21, wherein the fluoride-containing binderpolymer comprises polyvinylidene fluoride.
 23. The secondary batteryaccording to claim 1, wherein the insulation coating layer comprises theinorganic filler and the binder at a weight ratio of 5:95-80:20.
 24. Thesecondary battery according to claim 1, wherein the electrode tab is apositive electrode tab.